I have recently changed the bath and taps in my bathroom from a pair of taps to single mixer taps. Since doing this I noticed that the hot water only trickles out, the cold water is very powerful, so to fill up a nice warm bath it would take at least an hour and by then the hot water would have probably gone cold!
We have a standard boiler (not combi boiler) with a hot water tank in the airing cupboard on the first floor and a cold water reservoir in the loft.
We don't seem to have had this problem with the old taps, but I never had a bath (just showers-from electric shower over bath-no problem with temp for this) so I don't know what the water was like out of the old pair of taps.
Does anyone know how this can be solved? Is there different sorts of mixer taps? Therefore have I bought the wrong ones? Or is there a problem with my hot water system?
Thanks in advance for your help

The evidence suggests a problem at the new faucet. What brand is it? Are there integral stops [valves connected at the faucet connections]? Did you flush out any debris from the new faucet after installation? Some of the new single handle faucets clog easily and the cartridge seems to fail. Many times these cartridges can be rinsed clean. Was the single handle faucet professionally installed? If so, get him back out to warranty this thing.
You said the hot water is trickling out. I am guessing that when you turn it all the way over the water stream is very poor. If not, you may need to simply adjust the scaldguard limiter under the handle. The limiter does not allow the handle to turn far enough to open the hot water but rather stops the handle short. Hopefully you kept the paperwork on the new faucet and can try to adjust the limiter.